A biological tissue of a multicellular organism maintains a harmonious function as a whole by various cells taking on different roles. Once some cells become cancerous (hereinafter collectively referred to as a cancer, including a tumor), the cells grow into neoplasm different from its peripheral region. However, the cancerous region and a normal tissue region far away from the cancerous region are not necessarily distinguished by a certain borderline, and the peripheral region surrounding the cancerous region is affected to some extent. Therefore, in order to analyze a function of an organ tissue, it is necessary to separate a small number of cells present in a small region as easily as possible with minimal loss for a short time.
In the field of regeneration medicine, an attempt is being made to separate an organ stem cell from a tissue, reculture the stem cell, and induce the differentiation of the stem cell to regenerate a target tissue, and furthermore an organ.
To identify or separate cells, it is necessary to distinguish the cells according to a certain index. Common methods of distinguishing cells include the following:    1) Morphological cell classification based on visual observation: Examples include an examination for bladder cancer, urethral cancer and the like by an examination for atypical cells present in urine, and a cancer screening by classification of atypical cells in blood or cytological diagnosis in a tissue.    2) Cell classification based on cell surface antigen (marker) staining by a fluorescent antibody method: This is to stain a cell surface antigen, generally called as a CD marker, with a fluorescent labeling antibody specific thereto, and is used, for example for cell separation using a cell sorter, and a cancer screening using a flow cytometer or tissue staining. Naturally, these are frequently used not only in the medical field but also for the cytophysiological study and the industrial use of cells.    3) Alternatively, for separation of stem cells, fluorescent pigments designed to be taken into cells are used as reporters to roughly separate cells including stem cells and further then actually culture the cells, thereby separating target stem cells. Since an effective marker for a stem cell has not yet been established, the target cells are substantially separated by making use of only cells whose differentialtion has been induced by their actual culture.
Separating and collecting specific cells in a culture medium in this manner is an important technique for biological and medical analyses. When cells are separated based on a difference in the specific gravity of the cells, the target cells can be separated by a velocity sedimentation method. However, when there is little difference in the specific gravity of the cells that allows distinguishing between a non-sensitized cell and a sensitized cell, it is necessary to separate the cells one by one based on information from staining with a fluorescent antibody or information from visual observation.
This technique may be represented by, for instance, a cell sorter. The cell sorter is a technique in which a cell after fluorescent staining processing is dropped in a charged droplet as isolated one by one, and a high electric field is applied in any direction on the plane normal to the dropping direction in the process of the droplet dropping, where the dropping direction of the droplet is controlled by the applied voltage, based on the presence or absence of the fluorescence in the cell in the droplet and the amount of light scattering, to fractionate and collect the droplet in a plurality of containers placed at the bottom (Non Patent Literature 1: Kamarck, M. E., Methods Enzymol. Vol. 151, p 150-165 (1987)).
However, this technique involves the following problems: the cost is high; the system is large; a high electric field of some thousand volts is required; a large amount of samples concentrated to a certain concentration or more is required; cells may be damaged in the process of generating droplets; the samples cannot be directly observed. To solve these problems, a cell sorter has been recently developed which generates a fine flow path using microfabrication technology and separates cells flowing through the laminar flow in the flow path while directly observing the cells under a microscope (Non Patent Literature 2: Micro Total Analysis, 98, pp. 77-80 (Kluwer Academic Publishers, 1998)), Non Patent Literature 3: Analytical Chemistry, 70, pp. 1909-1915 (1998)). However, the following problems occur. Since the cell sorter which generates a fine flow path using the microfabrication technology is slow in the response speed of the sample separation with respect to an observation unit, another processing method that does not damage the samples and is faster in response is required in order to put the cell sorter into practical use. Further, the separation efficiency of the device cannot be improved sufficiently at a low cell concentration unless the concentration of the cells in a sample solution used is increased in advance to a predetermined concentration or more. Furthermore, when the cells are concentrated in a very small amount of a sample using a separated device, it is difficult to collect the concentrated solution without loss and at the same time the cells are contaminated at a cumbersome preprocessing stage, which is undesirable in regeneration medicine and the like.
In order to solve the problems, the present inventors have developed a device for cell analysis and separation capable of fractionating samples based on fine structures of the samples and fluorescence distribution in the samples and easily analyzing and separating the cell samples without damaging the samples collected, by utilizing microfabrication technology (Patent Literature 1: Japanese Patent Laid-Open No. 2003-107099, Patent Literature 2: Japanese Patent Laid-Open No. 2004-85323, Patent Literature 3: International Publication No. WO 2004/101731). This device is a sufficiently practical cell sorter at a laboratory level. However, for its versatile use in regeneration medicine, it is necessary to develop new techniques for a liquid transport method, a colletion method, and preprocessing such as sample preparation.